The technology of the 1 amp hour V-420 Lithium charger is designed primarily for use in charging Vexilar Lithium batteries, it is the first charger we know that is capable of charging both Lithium and SLA batteries very well. The easy to use charger lights show green when you have power and when battery is fully charged. Red tells you the charging cycle has engaged. A blinking red light will warn you that the battery is cold or terminal polarity is reversed.